The present invention relates to the field of semiconductor devices. More specifically, it relates to fabrication of buried gate insulator field effect transistors.
Most insulated gate field effect transistors in use today are fabricated of silicon. This is because silicon dioxide, which acts very effectively as the gate insulator, offers a well behaved transition from the silicon semiconductor and is physically and chemically stable throughout the series of processing steps necessary to fabricate the transistor. When used as a gate insulator, silicon dioxide is formed by the thermal oxidation technique. Silicon dioxide gate insulators formed by all other techniques have not proved to be as useful as those grown thermally, and as a result their use has been abandoned.
Other semiconductor materials offer attractive properties for use in field effect transistors. Their oxides and other dielectric compounds could act as gate insulators and also offer similar well behaved transitions. However, their use as field effect transistors has been restricted because their oxides and other dielectric compounds could not be thermally grown in a similar manner as silicon dioxide. This was primarily due to the fact that these dielectric materials could not be formed and retained in a physical or chemically stable manner throughout the series of steps necessary in transistor fabrication.
The elemental semiconductor germanium, for example, has an electron mobility of 3900 cm2/Vsec, more than double that of silicon. Its use could enable fabrication of devices with significantly higher processing speed. Other semiconductor materials that could be used are from the Group consisting of carbon, silicon carbide, and compound semiconductors of Group III and V elements, Group II and IV elements, Group II and VI elements, Group IV and VI elements, Group II and V elements, Group V and VI elements, Group V and VIII elements, or Group III and VI elements. If a way could be found to form solid phase gate dielectrics from these semiconductors, and provide protection to these novel dielectric compounds during the fabrication of the transistor it would satisfy a long-felt-need in the field of microelectronic device fabrication.